The invention relates to a dual clutch transmission, in particular of a motor vehicle, with a hydraulic circuit for cooling the dual clutch transmission, having at least one pump for conveying a hydraulic medium flow, at least one cooler for cooling the hydraulic medium flow, and a volume control valve for adjusting the hydraulic medium flow for at least one cooling system associated with the clutches of the dual clutch transmission.
The invention further relates to a method for operating a dual clutch transmission, in particular as described above, with a hydraulic circuit for the cooling of the dual clutch transmission, wherein a hydraulic medium flow is conveyed with a pump and cooled by a cooler, and wherein the hydraulic medium flow for at least one cooling system associated the dual clutch transmission is adjusted by a volume control valve.
Dual clutch transmissions are preferably used in passenger cars. A dual clutch transmission generally has two coaxially disposed transmission input shafts, wherein each is associated with a corresponding sub-transmission. A clutch is associated with each of the transmission input shafts, with which the transmission input shaft of the respective sub-transmission can be frictionally coupled to the output of an engine, preferably an internal combustion engine of a motor vehicle.
Typically, one of the sub-transmissions is active while driving, which means that the transmission input shaft associated with this sub-transmission is coupled to the engine via its associated clutch. A gear providing a current gear ratio is engaged in the active sub-transmission. A controller determines whether the next higher or next lower gear is to be engaged depending on the driving situation. This gear which will probably be used next is selected in the second, inactive sub-transmission. When changing gears, the clutch of the inactive sub-transmission is engaged, while the clutch of the active portion is disengaged. Preferably, opening of the clutch of the active sub-transmission and closing of the clutch of the inactive sub-transmission overlap so that the flow of force from the engine to the drive shaft of the motor vehicle is not at all or only briefly interrupted. As a result of the gear change, the previously active sub-transmission becomes inactive, while the previously inactive sub-transmission becomes the active sub-transmission. Thereafter, the gear expected to be used next can be engaged in the now inactive sub-transmission. The operation of a dual clutch transmission is otherwise known and will therefore be discussed here in detail.
Usually, the cooling systems of the clutches are served by a fixed displacement pump driven by an internal combustion motor. At least one control or regulating valve is used for adequate cooling of the clutch. The accuracy of the volume flow used for cooling the clutch depends strongly on the employed control or regulating valve. Typically, the hydraulic medium conveyed by the pump is cooled by a cooler and subsequently supplied to the cooling system associated with the clutches, so that only a single cooling medium volume flow is provided for the two clutches. The common cooling system for the clutches thereby worsens the control performance of the clutches.